Advice for mixed cells in pack

So this might sound a little cheap for lack of a better word, but for those of you who recycle or rebuild packs, do you have any advice for preventing rust/corrosion on 18650s after theyve been scuffed or tab welded a couple times?

If you leave most of the original nickel on re-used cells, they should remain rust resistant,. If you pull off the nickel, and grind them flat, you remove the nickel plating over the steel and they will rust.

docw009 said:

If you leave most of the original nickel on re-used cells, they should remain rust resistant,. If you pull off the nickel, and grind them flat, you remove the nickel plating over the steel and they will rust.

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yes i made this mistake. ive had some success going back over the scuffed ends with fine wet/dry and then the dremel with a buffing wheel with jewlers rouge ... so polishing the ends. thia reduces rust significantly, but its time consuming.

pack building is already a time-expensive task, so its worth seeking alternatives here.

what about painting or apraying with an anticorrosive after the pack is tabbed up? i believe ospho is conductive, but what about other anti corrosion finishes?

would it hurt the 18650s if i poured or sprayed over the pack top and bottom with flex seal? this would essentially cover the surfaces and fill any airgaps on the positive term with a latex like material.

other suggestions ive gotten are petroleum jelly or a wipe over with some oil on a rag, presumably after build.

Anyone got any feedback/ideas here?

docw009 said:

If you leave most of the original nickel on re-used cells, they should remain rust resistant,. If you pull off the nickel, and grind them flat, you remove the nickel plating over the steel and they will rust.

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when yall saY leave the original nickel in place, are you just cutting the strips between the batteries and laying new nickel over it or somehow splicing these nickel patches or whats it look like? Im having trouble imagining how yall leave most.of that stiff im place and the pack still look good or have evwn resistance from row to row given the variance ive seem in quality and type of tabs in OEM packs.

js1pxl11 said:

when yall saY leave the original nickel in place, are you just cutting the strips between the batteries and laying new nickel over it or somehow splicing these nickel patches or whats it look like? Im having trouble imagining how yall leave most.of that stiff im place and the pack still look good or have evwn resistance from row to row given the variance ive seem in quality and type of tabs in OEM packs.

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One can just skip the old nickel connections with scissors, trim the old nickel tabs to an appropriately short length, and then spot weld new nickel on top of the old tabs.

Nickel to nickel weld joints are not as a strong as the nickel to steel joints you get when welding to a cell casing, but it’s probably no issue for common ebike applications.

There is some finesse in removing old nickel. If the battery used very thick nickel, try rotating it around the welds. Often this breaks the welds without denting the can.
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What about variance in mAh when gathering lots of cells? In, for example, a 10s4p ebike with a 350w motor, what is an acceptable gap bw the lowest mAh in each parallel group and the highest, or if resistance is better, whats acceptable within parallel groups and whats acceptable overall in the pack min/max or mean deviation? Love to hear some experienced thoughts on this topic?

docw009 said:

There is some finesse in removing old nickel. If the battery used very thick nickel, try rotating it around the welds. Often this breaks the welds without denting the can.
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The twist is a good tip.. Thanks for that.

js1pxl11 said:

What about variance in mAh when gathering lots of cells? In, for example, a 10s4p ebike with a 350w motor, what is an acceptable gap bw the lowest mAh in each parallel group and the highest, or if resistance is better, whats acceptable within parallel groups and whats acceptable overall in the pack min/max or mean deviation? Love to hear some experienced thoughts on this topic?

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Recently discussed in a previous thread:
"Acceptable" is relatively, depending on use case and intended application. My stationary powerwall home backup have variance of like 500mah between the highest and lowest capacity cells, because it's not a high-drain battery. I wouldn't stray more than 50-100mah in a high-discharge pack.

for stoping corosion with my homemade packs i normaly use a paintbrush dipped in new engine oil and paint over the welds,for waterproofing the bms plugs i smotherthem in grease then the whole lot is wrapped in black gaffa tape,had a pack like this for 5 yrs and its still ok.,gaffa tape is cheaper than shrinkwrap.

I scuff away bad cells or cells I'm unsure off.

A good outer shell is something to ponder about or go commando without an outer shell but some chock protection and tape.

I also don't know but gluing them in could maybe solve this rust issue but cause others ones as time goes by.